This invention relates to nuclear reactors, and, more particularly, to insulating and shielding the reactor vessels of such reactors.
It is standard practice for the reactor vessels of nuclear reactors to be surrounded by a primary shield which assists in shielding the area surrounding the vessel from radiation emitted from the reactor vessel. Typically, there is a small amount of space, or volume, between the reactor vessel and the inner wall of the primary shield. The size of the space depends upon the size of the gap between the reactor vessel and the primary shield. Primary shields have traditionally been made of concrete. The designs or configurations of primary shields have typically been controlled by the amount of radiation shielding which must be maintained. The high temperatures associated with the reactor vessel during operation, typically on the order of 500.degree. to 600.degree. F. may result in deterioration of the portion of the primary shield adjacent to the reactor vessel. To lessen the likelihood of deterioration of the primary shield, it is desirable to keep the temperature thereof from exceeding about 150.degree. to 200.degree. F. Accordingly, it is necessary to thermally insulate the reactor vessel from the primary shield.
Traditionally, the reactor vessel is disposed within a generally cylindrical opening in the primary shield with approximately a 6 to 10 inch annulus, or gap, between the reactor vessel and the primary shield. The reactor vessel insulation has typically been attached directly to the reactor vessel during construction of the reactor facility. Subsequent removal or replacement of the insulation has been very difficult and time consuming because of the limited amount of space between the reactor vessel and the primary shield. It has been known to increase the size of the gap between the cylindrical reactor vessel and the cylindrical primary shield to increase the amount of space therebetween, and thereby enhance accessibility of the insulation. However, this approach has proven to be an unsatisfactory solution because it requires increasing the distance which must be spanned by the reactor vessel supports which support the reactor vessel in the primary shield.
It would also be desirable to increase the amount of space between the primary shield and the reactor vessel in order to provide more space for external reactor monitoring instruments, such as excore detectors. In existing reactors, such detectors are positioned within the space between the reactor and the primary shield, or within the concrete of the primary shield. With either of these types of excore detector installation, the reactor vessel insulation is disposed between the reactor vessel and the excore detectors. The presence of such insulation may adversely affect the operational performance of the excore detectors because the strength of the signal being monitored by the excore detectors may be reduced by the signal's passage through the insulation.
There is a need for a nuclear reactor wherein additional space is provided between the reactor vessel and primary shield for installation, removal and maintenance of the reactor vessel insulation, and for accommodation of and improved access to reactor monitoring instrumentation, but which does not require the reactor vessel supports to span increased distance, or gap, to accommodate such increased space.